Re-posted following a reading of the relevant FAQ
Dear Statalisters,
(I am using Stata/MP v10.1, born 02 Feb 2009)
It was my belief that the regression estimates from a multinomial logistic
regression model -mlogit- could be replicated through a set of simple logit
models with the appropriately derived binary outcomes.
Whilst attempting to demonstrate this fact for some teaching material on
polytomous IRT that i am writing, I moved from my usual categorical
predictors to a continuous covariate + discovered that the above equivalence
no longer held.
for instance, with a 4-level outcome (ghq1) and either a binary predictor
(ghq3_bin) or a 4-level predictor treated as a continuous variable (ghq3),
I fitted models with the two commands
******************************
mlogit ghq1 ghq3_bin, baseoutcome(0)
mlogit ghq1 ghq3, baseoutcome(0)
******************************
the former can be replicated using logits, whilst the latter cannot.
I am struggling to understand why this should be.
I would very much appreciate any advice you can give,
Jon
--
Dr Jon Heron
ALSPAC Stats Team Leader
Department of Social Medicine
University of Bristol
Oakfield House
Oakfield Grove
Bristol
BS8 2BN
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
